The Permian mass extinction was the most severe extinction event in the history of life, killing an estimated 90% of all species. However, its causes remain mysterious. Using fossil data from the Karoo Basin in South Africa, we construct a food web model of Permian ecosystems before the extinction event. We group fossil species into 22 guilds based on their ecological roles and use a paleobiological computer model to simulate perturbations to these food webs. We then use Markov Chain Monte Carlo techniques, specifically the Metropolis-Hastings Algorithm, to construct a Bayesian posterior distribution for the various extinction-event scenarios, thereby inferring the initial level of extinction in each guild.

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